Really bad idea. Breaks all kinds of code rules.

The double pole breaker won't protect you, the only protection would be at the generator with its breaker. If you are bringing in 120vac, then bring it in on a single pole breaker.

It would technically work, but if you left any of the double pole breakers on in the house with appliances connected you would have problems.

For a situation like yours, I would get some lockout-tagout locks for all of your double pole breakers and put them on before connecting the generator. Also, I would modify a dryer plug to do the bridging rather than hard wire it on the generator connection... and label it for emergency use only. That would be the only double pole breaker to leave on.

None of the above would pass an inspection.

https://smile.amazon.com/dp/B085DCQR6X is an example of a breaker lockout